1. Field of the Invention
The present invention relates to an intake duct structure in a vehicle, such as a motorcycle or the like.
2. Description of Background Art
A conventionally known intake duct structure includes an intake duct extending forwardly from an air cleaner box, wherein the intake duct is made to open forward of the vehicle in an area downward of a head pipe of a vehicle body frame. Running wind is thereby introduced into the air cleaner box and a running wind pressure involved therewith is used as a boost pressure. The arrangement is known what is called as ram pressure boost (see, for example, Japanese Patent Laid-Open No. 2004-301024). This intake duct structure includes a valve for selecting either one of two intake paths. The valve is disposed in the intake duct and driven by a motor-driven actuator according to an engine speed.
Against the aforementioned conventional structure, an arrangement is known that includes an intake duct disposed so as to penetrate through an area near a head pipe of a vehicle body frame and made to open forwardly at a front end portion of a front cowl. While allowing the running wind to be more readily guided into the air cleaner box, this arrangement also lets rainwater and the like enter easily. Accordingly, it is desirable that a valve as described above be provided in the intake duct. It is also preferable that a driving mechanism for the valve be made simple, considering the arrangement, in which the valve is disposed forward of the head pipe.